(a) Field of the Invention
The present invention relates to an afocal zoom lens system and, more particularly, to an afocal zoom lens system to be used with microscopes and the like.
(b) Description of the Prior Art
Many zoom lens systems with comparatively low magnifications to be used with stereomicroscopes, operation microscopes, etc. are known, for example, as disclosed in Japanese published examined patent applications Nos. 31259/73, 2916/69, 18356/68, 12714/68 and so forth. Though the zoom lens systems disclosed in said patent applications have individually different zoom ratios, they are all converging optical systems and, therefore, it is impossible to use them in combination with a photographing device, television device, incident light illumination device provided coaxially with the optical axis of an observation optical system, etc.
Besides, afocal zoom lens systems for photographic cameras are known, for example, as disclosed in Japanese published examined patent applications Nos. 41402/80, 40849/80, 9094/78 and No. 13663/76. However, none of the zoom lens systems desclosed in said patent applications have sufficiently large zoom ratio.